A lithography technique for reducing and transferring various patterns formed on a mask onto a wafer with light is used to manufacture semiconductor devices. A mask pattern for use in lithography is required to have an extremely high degree of accuracy. Hence, to form a mask pattern, an electron beam exposure apparatus capable of drawing fine patterns is employed. An electron beam exposure apparatus is also employed to directly draw a fine pattern on a wafer without any masks.
Electron beam exposure apparatuses include, e.g., a point-beam type apparatus which uses spot-like beams and a variable rectangular beam type apparatus which uses beams each having a variable-size rectangular cross section. A general electron beam exposure apparatus comprises an electron gun portion which generates electron beams, an electron optical system for guiding electron beams emitted from the electron gun portion onto a sample, a stage system for scanning the entire surface of the sample with electron beams, and an objective deflector for positioning electron beams on the sample at high accuracy.
A region in which the objective deflector can position electron beams needs to have a width of about several mm in order to minimize any aberrations in an electron optical system. As for the size of the sample, when a silicon wafer is employed as the sample, its diameter is about 200 to 300 mmφ. As for the size of a glass substrate to be used as a mask, its size is about 150 mm square. For this reason, a stage which enables scanning of the entire surface of the sample with electron beams is adopted.
To perform high-accuracy exposure, any shift in posture and position of the stage are measured. Since the response of positioning electron beams is extremely high, the amount of shift is generally adjusted not by using a system arrangement for improving the mechanical and control characteristics of the stage but by positioning electron beams with a deflector which deflects the electron beams.
Hence, a conventional stage only has to move in the direction of the X-Y plane. Additionally, a conventional stage has certain constraints, i.e., the stage must be arranged in a vacuum chamber and is not allowed to cause any variation in magnetic field, which may affect the positioning of electron beams. For this reason, a conventional stage comprises limited contact mechanism elements such as a rolling guide, ball screw actuator, and the like.
However, a contact mechanical element suffers from problems about lubrication, particles, and the like. To solve such problems, there is disclosed an X-Y transfer stage comprising a stage arrangement which includes a vacuum air guide and a linear motor, and has two degrees of freedom in a plane direction, as shown in FIG. 5. According to the stage arrangement of FIG. 5, a stage can accelerate extremely smoothly in the X and Y directions and the stage can be hardly disturbed by a guide in alignment in the X and Y directions.
An electron beam exposure apparatus must have a higher speed (throughput) in lithography. To achieve this, there is disclosed, e.g., a multi electron beam exposure apparatus which irradiates the surface of a sample with a plurality of electron beams in accordance with design coordinates, scans the sample surface by deflecting the plurality of electron beams in accordance with the design coordinates, and individually turns on/off the plurality of electron beams in accordance with a pattern to be drawn, as disclosed in Japanese Patent Laid-Open No. 9-330867. A multi electron beam exposure apparatus can draw an arbitrary pattern with a plurality of electron beams and thus can increase the throughput.
FIG. 6 is a view showing the outline of a multi electron beam exposure apparatus. Electron guns 501a, 501b, and 501c can individually turn on/off electron beams. A reduction electron optical system 502 reduces and projects a plurality of electron beams from the electron guns 501a, 501b, and 501c onto a wafer 503. A deflector 504 deflects the plurality of reduced and projected electron beams onto the wafer 503.
FIG. 7 shows how the multi electron beam exposure apparatus of FIG. 6 scans a wafer with a plurality of electron beams. White circles represent beam reference positions (BS1, BS2, and BS3) at which each electron beam comes incident on the wafer when it is not deflected by the deflector 504. The beam reference positions (BS1, BS2, and BS3) are plotted along a design orthogonal coordinate system (Xs,Ys). The respective electron beams move along the design orthogonal coordinate system (Xs,Ys) with reference to the beam reference positions (BS1, BS2, and BS3) and scan exposure fields (EF1, EF2, and EF3) for the respective electron beams. The exposure fields for the respective electron-beams are arranged adjacent to each other. By sequentially exposing these exposure fields, the exposure fields over the entire wafer are exposed. However, since lithography requires higher accuracy and higher speed, it is necessary to suppress a degradation in drawing accuracy due to the yawing component of a stage supporting a substrate.
To this end, there is available a method of correcting a yawing component using a deflector in an electron beam exposure apparatus. Even with this method, a correction control system using a deflector inevitably becomes complicated, thus resulting in an increase in cost and a decrease in throughput. Though a conventional stage arrangement has excellent alignment characteristics in the X and Y directions, it is difficult to greatly reduce a yawing component.
If scanning and exposure are performed in a stage by a multi electron beam exposure scheme, a yawing component is more likely to occur as a positional shift from each beam than by a single-beam exposure scheme such as a point-beam type exposure scheme, variable rectangular beam type exposure scheme, or the like.
More specifically, in a conventional single-beam exposure apparatus, a beam position is located at the intersection point of measurement axes for measuring the position of a stage in two axial directions on a plane. For this reason, a shift in the plane direction due to a distance from the beam position regardless of the position of the rotation center of yawing is automatically corrected by position feedback. If part of the shift is left uncorrected, a deflector may correct the part as a stage positional shift. In this case, a rotation component will be left uncorrected. Assume that the size of an exposure field is 10 μm square, and that a 100-μrad stage rotates. In this case, though a positional shift of up to 1 nm may occur in the in-plane direction of a wafer within a drawing spot, this shift can be neglected.
Consider the case of a multi electron beam exposure apparatus using a plurality of beams. For example, if the plurality of beams comprises two beams, and a distance between the beams is 10 mm, only one beam can be positioned at the intersection point of the measurement axes. As for one beam, a positional shift from a beam position at the intersection point is the same as that described in the case of a single-beam exposure apparatus. As for the other beam, a positional shift occurs in accordance with a distance from the intersection point of the measurement axes. If a 100- μ rad stage rotates with the above-mentioned beam distance, a difference between the positional shift amounts of the respective beams becomes 1000 nm.
To correct these positional shift amounts, rotation correction may collectively be performed for all the beams by a rotary deflector or correction may separately be performed for the beams by respective deflectors. Either method, however, inevitably has a complicated control system, thus resulting in an increase in cost and a decrease in throughput.
Under the circumstances, there is a need for an electron beam exposure apparatus having high-frequency band control characteristics in the yawing direction of a stage in order to reduce a degradation in drawing accuracy due to the yawing component of the stage and to realize high-accuracy exposure.